• Cory Fields proposed a Bitcoin quantum-landmine concept that requires attackers to provide matching collateral.
  • The mechanism uses a hidden proof and a 30-day example challenge period to let owners reclaim vulnerable BTC.
  • Lost wallets remain unprotected, and the proposal still needs new validation rules.

A future quantum attacker might need more than a vulnerable Bitcoin key to steal legacy coins. Under a proposed experiment from Bitcoin Core developer Cory Fields, anyone attempting to spend vulnerable Bitcoin would also have to provide matching collateral. 

Fields posted the concept to the Bitcoin-dev mailing list. He described it as a thought experiment that assumes quantum-safe outputs and new validation rules after a hypothetical “Q-day.” It is not a Bitcoin network upgrade.

A Hidden Trap Could Change the Attacker’s Calculation

In Fields’ example, a Bitcoin owner prepares for a potential quantum attack by creating a small quantum-safe output containing a hidden proof linked to their vulnerable Bitcoin. If an attacker tries to spend the owner’s 1 BTC, they must provide another 1 BTC of their own as collateral. The two amounts are then locked together for a set period, with Fields using 30 days as an example.

During that period, the owner could reveal the precommitted proof, move the coins to a designated quantum-safe key, and claim the attacker’s collateral. The commitment would remain hidden, leaving an attacker unable to know which vulnerable holdings had been prepared.

An attacker would weigh the target’s value against the possibility of losing an equal stake. The deterrence would depend on how many owners prepared, whether they retained their keys, and whether they responded before the lock expired. Fields said the arrangement could encourage owners to bait an attacker because a valid claim would include the collateral.

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Matching Collateral Could Burden Legitimate Holders

The collateral rule would apply to legitimate holders, too. To move 1 BTC from a vulnerable output, an owner would need another 1 BTC in a quantum-safe output, temporarily tying up both amounts. The same rule that raises attack costs could restrict an unbiased holder’s access to funds.

Lost wallets create another gap. Owners without access to their keys could not reveal proof during the challenge period, so a landmine could not protect those coins. Fields separately explored auction-based mechanisms for vulnerable coins whose owners may have lost access to their keys. These included a staked auction and a Sats Auction, although their rules and implementation remain unsettled.

The proposal leaves several design questions open, including collateral ratios, waiting periods, and how legitimate owners would be distinguished from attackers. Fields also said he had not settled on the desired outcome. Until the necessary validation rules and implementation details are developed, quantum landmines remain a thought experiment rather than a change to Bitcoin’s rules.

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Related: Bitcoin’s Quantum-Resistance Roadmap Is Taking Shape

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